1. Field of the Invention
The present invention relates to light control film and in particular to light control film that reduces glare.
2. Description of the Prior Art
Luminous displays, for example, televisions, computer monitors and LED calculator displays, are a popular means of supplying visual information. One major shortcoming of these displays is a tendency to reflect light from other sources back to an observer. These reflections are commonly known as "glare" and interfere with the perception of the luminous display.
One approach to preventing or controlling glare is the use of a polarizing film, since reflected light is generally partially polarized. The polarizing film may be oriented to minimize transmission of light polarized in a first direction. However, the polarized film remains transmissive to light polarized in a second direction, perpendicular to the first direction. Thus, some reflected light passes through the film and this approach has limited utility.
U.S. Pat. No. 4,604,297 to Liu discloses a method of controlling light transmission through a reflective/transmissive surface by first creating surface irregularities having an anti-glare effect and then applying an inert liquid coating sufficiently thick to remove at least some, but not all, of the anti-glare effect. The surface irregularities are created by applying a dispersion and allowing it to dry to form a coating that reduces reflective glare at the surface. This patent discusses the problem of surface glare on computer monitors, and allowing light to pass from the viewing surface to the viewer.
Other approaches to controlling the passage of light through a film include U.S. Pat. No. 3,919,559 to Stevens which teaches a process for producing a film including radio-opaque, louvre-like elements of divergent or convergent orientation. Pairs of the films may be used to form Bucky grids for x-rays. U.S. Pat. No. 3,922,440 to Wegwerth et al. teaches a light control film with louvers which is bonded to a transparent protective covering material. U.S. Pat. No. 4,128,685 to Lowrey et al. discloses a skivable billet having an improved uniform heat absorption ability in which layers of enhanced optical density comprise water soluble polyazo direct dyes such as Formanil Black G and finely divided silica.
U.S. Pat. No. 3,222,515 to Orr discloses an apparatus for controlling the dispersion of light from a localized source such as a fluorescent tube. The device includes a film approximately 2 mils thick with aligned air spaces or bubbles which reflect at one angle and transmit at another angle.
Another body of art relates to devices that require the presence of an external electric or magnetic field for function. U.S. Pat. No. 1,955,923 to Land discloses a light valve and a method of operating the light valve. The disclosed light valve includes a light-transmitting fluid-suspending medium having a dispersed suspension of polarizing particles therein, showing Brownian movement and susceptible to an electrically controlled field of force and means adapted for applying such a field to said particles, i.e. an electric or a magnetic field.
One embodiment of the light valve comprises a container and a suspension of particles susceptible to a magnetic field.
U.S. Pat. No. 3,341,247 to Marks discloses an electrically responsive light control device employing suspended dipole particles within liquid droplets enclosed in a plastic film. The particles may be temporarily aligned by an electric field to either reflect or transmit light.
The dipole particles of Marks are preferably about 2,000 to 3,500 Angstroms in length, and their cross sectional width is about 200 to 700 Angstroms. These dimensions are necessary, according to Marks, to allow the dipole particles to effectively reflect or scatter visible light incident upon them at an angle of approximately plus or minus 40.degree. to the normal of their longitudinal axis and to add substantially no reflectivity or scatter at other angles. Marks also teaches that larger particles, up to about 50 microns in diameter by about one micron thick may be employed where light scatter is not objectionable.
The prior art has failed to recognize the desirability of a light control film comprised of polarizable particles that do not require the presence of an external electric or magnetic field for their operation. Furthermore, the art has failed to provide an article, such as a film, for use on a luminous display which reduces glare originating from multiple sources, such as side and overhead lighting, while remaining generally transmissive to light emitted from the luminous display in a direction normal to the face of the display. This failure of the prior art has been overcome in the present invention by providing a plurality of opaque aciculae or whiskers, locked in a transparent matrix in an orientation such that the longitudinal axis of each acicula is generally parallel to the direction of desired light passage.